This invention generally relates to alkenyl aromatic polymer foam laminates, and in particular to alkenyl aromatic polymer foam laminates that have a facer adhered to at least one, preferably both, major planar surfaces of an alkenyl aromatic polymer foam core. The resulting laminates exhibit improved stiffness and impact resistance relative to the alkenyl aromatic polymer foam core alone. The invention relates more particularly to alkenyl polymer foam laminates wherein the facer has an enhanced recyclability into the foam core relative to oriented polypropylene (OPP) film facers. The invention relates still more particularly to alkenyl polymer foam laminates that include an amount of recycled material.
In an attempt to improve thermal insulation of various building structures, common construction practice applies relatively thin (one-quarter inch or 6.4 millimeters (mm) to two inches (55 mm)) rectangular panels of foam board to of building structure walls. The building trade refers to such panels as xe2x80x9cresidential foam sheathingxe2x80x9d. Foam boards employed in such applications include those of extruded polystyrene foam, molded expanded polystyrene foam (also known as xe2x80x9cMEPSxe2x80x9d), and polyisocyanurate foam.
The thin foam boards, while improving thermal insulation performance of a building structure wall, are prone to physical damage from bending, impact, or breaking. Such damage may occur by a variety of means including acts of vandalism, high velocity winds, and construction practices. Ladders that lean against vertical walls tend to bend or break attached foam boards, especially with the added weight of construction personnel. Construction personnel who kneel upon foam boards attached to horizontal walls while such walls are being assembled prior to vertical erection also cause damage.
One proposal to lessen, if not eliminate, such physical damage involves applying a facing material (also known as a xe2x80x9cfacerxe2x80x9d) to at least one major planar or primary surface of a foam board to provide additional strength. Examples of such facing materials include thermoplastic films, metal foil, paper or thin cellulose films, non-woven polymeric fabrics, fiberglass scrims, and combinations of the foregoing. Extruded polystyrene and MEPS foam boards commercially use a thermoplastic film as facing material. Commercially used facing materials for extruded polystyrene, MEPS, and polyisocyanurate foam boards include metal foil, paper, fiberglass scrims, and combinations thereof.
The various facing materials have their own unique advantages and disadvantages. Plastic film has the advantage of easy application, economical cost, and optional transparency. Metal foil has the advantages of easy application, vapor barrier resistance and infrared and ultraviolet reflectivity. Fiberglass scrim has the advantage of excellent strength, but is relatively expensive, and causes a significant amount of itching and discomfort to construction personnel during installation. Metal foil can be easily punctured, and may have a very reflective surface that reflects sunlight back into the faces of those installing the insulation. Plastic film facers can be less effective in adding strength and stiffness to the foam.
Applying a thermoplastic facer film to polystyrene foam boards used in residential sheathing applications provides some help, but leaves the resulting laminates subject to fracture problems from bending and impact. One explanation for the fracture problems suggests that the boards lack sufficient thickness in that they typically range in thickness from 0.5 inch (12.7 mm) to 1.0 inch (25 mm). In addition, the facer films may be too thin (from 0.5 mil (13 micrometers (xcexcm) to about 2.0 mils (50 xcexcm)) and have insufficient tensile strength.
Fractures may form in the foam board from either compressive or tensile stresses. Fractures typically propagate from non-laminated board surfaces and from foam panel/facer film interfaces in laminated boards. Compressive stresses occur at a foam panel surface or at an interface between a foam panel surface and a facer film in response to an impact or an external force applied against the surface or interface. When the impact or applied external force places compressive stress on one panel surface or foam/film interface, it simultaneously causes application of tensile stress at a foam panel surface or foam/film interface on an opposing side of the foam board or laminate.
An improved laminated foam insulation board having enhanced strength and resistance to bending and breaking is disclosed in U.S. Pat. No. 5,695,870, assigned to The Dow Chemical Company, the assignee of the present invention. The insulation board includes a panel of a plastic foam material and first and second thermoplastic facers adhered to both primary surfaces of the panel. Each facer has an ultimate elongation of less than ( less than ) 200 percent (%) in both machine and transverse directions, a yield strength of at least (xe2x89xa7) 7,000 pounds per square inch (psi) (48,400 (kilopascals kPa)) in both machine and transverse directions, and a 1% secant modulus xe2x89xa7200,000 psi (1,380 megapascals (mPa)) in both machine and transverse directions. The degree of adhesion between each of the facers and the foam panel is expressed as a peel strength xe2x89xa7100 grams per inch (g/in)(39.4 grams per centimeter (g/cm)). Determine peel strength using a 180xc2x0 peel test (American Society for Testing and Materials ASTM) test D-903. Suitable films having the required properties include biaxially oriented polyolefin, alkenyl aromatic polymer, polyester, polycarbonate, acrylic polymer, and polyamide films having a thickness of from 0.35 to 10 mils (10 to 250 xcexcm). The disclosed laminates exhibit significantly improved resistance to bending and breaking as compared with previously known insulation boards with facers that do not have the required elongation, yield strength, and 1% secant modulus.
Biaxially oriented polyolefin films and biaxially oriented polyester films provide laminated insulation foam boards with enhanced strength and resistance to breaking, but do so with an offsetting disadvantage. Only small amounts of these films and polyethylene films can easily be recycled back into foam boards prepared at least in part from an alkenyl aromatic polymer such as polystyrene. The amount of polypropylene, polyethylene or polyester film material present in scrap product often exceeds these small amounts. An attempt to exceed the small amounts adversely affects foam performance. Efforts to maintain foam performance lead to solutions such as discarding a portion of the scrapped product into landfill or removing the polyolefin or polyester film from the laminate to allow recycling of the polystyrene foam only. Discarding scrap product into landfill is undesirable because it increases the ultimate cost of the product by increasing the amount of unused waste materials, and because it adds to the ever-burgeoning amounts of solid waste which are depleting available landfill sites. Separating the excess amounts of polyolefin or polyester films from scrap product is also undesirable because it is relatively difficult and expensive. Other, more recyclable films, such as oriented polystyrene film, have suitable stiffness, but do not impart an impact resistance equivalent to that provided by the biaxially oriented polyolefin and biaxially oriented polyester films.
Accordingly, a need exists for an improved laminated insulating foam board that exhibits both the enhanced board strength and resistance to bending and breaking provided by the biaxially oriented polyolefin and biaxially oriented polyester films and an improvement in recyclability into foams made from alkenyl aromatic polymers relative to laminates made with such biaxially oriented facers.
The present invention is a laminated insulating foam board comprising a panel of a plastic foam material, and at least one thermoplastic facer adhered to at least one of the primary surface of the panel, the facer comprising a polymer blend containing an alkenyl aromatic polymer or copolymer, and an interpolymer having polymerized therein ethylene, one or more alkenyl aromatic monomers or hindered aliphatic or cycloaliphatic vinylidene monomers and, optionally, one or more copolymerizable olefinic monomers that contain from three to twenty carbon atoms (C3 to C20). The foam panel desirably has a thickness within a range of from 6 to 150 millimeters (mm), preferably from one-quarter inch (in) (6.4 mm) to four inches (100 mm). The polymer blend desirably contains from 98 to 30 percent by weight (wt %) alkenyl aromatic polymer and from 2 to 70 wt % interpolymer, both percentages being based on polymer blend weight and totaling 100 weight percent. The facer may be in the form of a continuous film, or in the form of a thin foam sheet. The resulting laminated insulating foam board of the invention exhibits excellent resistance to bending and breaking, and any scrap product can be more easily recycled back into the polyalkenyl aromatic materials used to form the panel of insulating foam without having to remove the facers. The facer preferably has sufficient compatibility with the foam material to allow recycling of the laminated insulating foam board, or components thereof, into the foam panel. A suitable recycle material content for a foam panel is from 1 to 50 percent by weight, based on foam panel weight.
The facer may be in the form of a continuous film or a thin foam sheet.